Harvesting energy from non-ideal vibrations

Abstract

Energy harvesting has drawn significant interest for its potential to power autonomous low-power applications. Vibration energy harvesting is particularly well suited to industrial condition sensing, environmental monitoring and household environments where low-level vibrations are commonly found. While significant progress has been made in making vibration harvesters more efficient, most designs are still based on a single constant vibration frequency. However, most vibration sources do not have a constant frequency nor a single harmonic. Therefore, the inability to deal with non-ideal vibration sources has become a major technological obstacle for vibration energy harvesters to be widely applicable. To advance the state of vibration energy harvesting, this thesis presents a design methodology that is capable of dealing with two major non-ideal vibration characteristics: single harmonic frequency shifting and multi-frequency/broadband excitation. This methodology includes a broad-band impedance matching theory and a power electronics architecture to implement that theory. The generalized impedance matching theory extends the well known single frequency impedance matching model to a multi-frequency impedance matching model. By connecting LC tank circuits to the harvester output, additional resonant frequencies are created thereby enabling the energy harvesting system to effectively harvest energy from multi-harmonic vibration sources. However, the required inductors in the LC tank circuits are often too large (>10 H) to be implemented with discrete components. The power electronics proposed here addresses this issue by synthesizing the tank circuits with a power factor correction (PFC) circuit. This circuit mainly consists of an H-bridge, which contains four FETs, and a control loop that turns the FETs on and off at the right time such that the load voltage and current display the characteristics of the multiple tank circuits. By using this proposed power electronics, we demonstrate dual-frequency energy harvesting from a single mechanically resonant harvester. Simulation and experimental results match well and demonstrate that the proposed power electronics is capable of implementing higher order multi-resonant energy harvesting systems. In conclusion, this thesis presents both a theoretical foundation and a power electronics architecture that enables simultaneous effective multi-frequency energy harvesting with a single mechanically resonant harvester. The tunability of the power electronics also provides the possibility of dynamic real-time tuning which is useful to track non-stationary vibration sources.